Effect pigments are used to introduce metallic or pearlescent luster to a wide range of products such as paints, coatings, inks, and plastics. Good passivation and dispersion of the metallic effect pigments are desirable for optimal performance of such products.
Metallic effect pigments, especially those that include aluminum, bronze, iron oxide and steel pigments, can react with water, acids or bases in coating or ink formulations. In the instance where the metallic effect pigments include iron oxide, a thermite reaction can occur, leading to the loss of physical properties. Passivation such as waterborne passivation of metallic effect pigments, particularly aluminum, bronze and steel pigments, can improve the durability of the pigments and their aesthetic effects. In some of the disclosed approaches, organophosphorous compounds are used during the passivation of metallic effect pigments.
Passivation of these pigments by the addition of phosphonic acid can prevent such losses in physical properties.
For example, U.S. Pat. No. 4,717,424 discloses passivation with phosphonic or phosphinic acids where the R group has a terminal COOH carboxylic acid group.
U.S. Pat. No. 4,565,716 discloses the passivation of metallic pigments using acidic phosphate esters, phosphonic acids or acidic phosphonic esters.
U.S. Pat. No. 7,462,394 discloses aluminum passivation from polymer containing both phosphoric or phosphonic acid groups and another substituent chosen from nitro, pyridine, or phenolic hydroxyl groups.
U.S. Pat. No. 5,091,451 discloses aluminum passivation from a compound which is a reaction product of an alpha-aminomethylene phosphonic acid and a compound containing at least one epoxy group.
U.S. Pat. No. 5,429,674 discloses passivation from a compound which is a reaction product of an N-acyl aminomethylene phosphonates.
While conventionally used organophosphorous reagents may impart chemical stability to the metallic pigment so as to address passivation, such reagents do not address the issues related to dispersion of the metallic effect pigments.
Optimal performance of products including metallic effect pigments also require the metallic effect pigments to be well dispersed. Well dispersed metallic effect pigments are desirable in the products to prevent agglomeration of the pigments, improve hiding and enhance aesthetics. Efforts have been made to encapsulate the metallic flakes with a polymer coating to improve dispersion of pigment flakes.
U.S. Pat. No. 7,479,323 for instance discloses pre-treating aluminum flakes with polyvinyl alcohol to improve the dispersion of pigments in aqueous media.
U.S. Pat. No. 4,213,886 discloses procedures to modify aluminum flakes with monoethylenically unsaturated silane.
However, while the incorporation of functional monomers into the polymer chains may improve the dispersion/compatibility of pigments inside an applied media, these functional groups may adversely affect the chemical resistance of the flakes.
In general, a combination of both good passivation and dispersion of metallic pigments has been difficult to achieve.